The properties of optical fiber make it an ideal medium for carrying signals in an ever-increasing number of applications. These properties include high bandwidth, i.e., signal-carrying capacity, immunity to interference, low loss, light weight and low bulk. Optical fiber is often used in conjunction with electrical leads which carry power, such as in the cables of many remotely operated systems. Undersea robots for tasks such as pipeline inspection, networked rotating industrial workstations, wireline logging systems for downhole measurements in wells, and material handling applications are examples of such systems. The cable is normally handled by a winch or reel. This requires a slip ring or rotary joint assembly to permit the paying out or retraction of the cable without interrupting signal connection to the remote system.
Slip rings for electrical wires are well established, but fiber optic rotary joints are much more recent developments. In many fiber optic systems more than one fiber is needed, for redundancy, bandwidth, or system cost considerations. Two is often the optimal number of fibers, such as in duplex networks or installations demanding a spare channel. Yet rotary joints for more than one fiber are not developed to an adequate state for many applications. Prior inventions require complex assemblies which variously employ optical components such as prisms, mirrors, cuspated lenses, axicons, infinite focal length ring lenses, or eccentric lenses, and mechanical elements such as gears and magnets. Consequently, commercially available multiple channel fiber optic rotary joints can be too large or delicate for some applications, or too costly for others. In addition to the kinds of applications listed above, a sufficiently small fiber optic rotary joint can be retrofitted into many existing installations such as antennas, turrets and winches. This permits the continued use of existing slip ring assemblies, greatly enhancing system operation at minimal cost. A fiber optic rotary joint which shares the miniature, low cost and robust characteristics of a single channel fiber optic rotary joint while accommodating at least two fibers could satisfy these applications.
A search has uncovered a number of US patents describing multiple channel fiber optic rotary joints, namely:
______________________________________ 4,519,670 Spinner et. al. LIGHT-ROTATION COUPLING FOR A PLURALITY OF CHANNELS 4,643,521 Harstead et. al. PLURAL-CHANNEL OPTICAL ROTARY JOINT 4,725,116 Spencer et. al. MULTIPLE PASS OPTICAL ROTARY JOINT 4,834,484 Gorman et. al. OPTICAL FIBER COUPLER INCLUDING REFRACTIVE MEANS FOR PRODUCING AN ANNULAR BEAM 4,961,622 Gorman et. al. OPTICAL COUPLER AND REFRACTIVE LAMP 4,842,355 Gold et. al. MULTICHANNEL OPTICAL ROTARY JOINT FOR WELL LOGGING USAGE 5,073,040 Guinard MECHANO-OPTICAL DEVICE, IN PARTICULAR A ROTARY OPTICAL JOINT 5,157,745 Ames MULTI-CHANNEL FIBER OPTICAL ROTARY JOINT FOR SINGLE-MODE FIBER ______________________________________
and one U.S. patent on single channel fiber optic rotary joints:
______________________________________ 4,398,791 Dorsey ______________________________________